Scientists say the long-term effects of the spill remain unknown — but oyster and crab catches are down, driving some long-time fisherman out of business.

Tam Huynh hauls a blue crab trap over the side of his boat, shakes the catch out of it and tosses it back overboard. The results are disappointing.

"See, the crab like that, you can feel it's so skinny," he says, pressing on a spot just behind the spines that jut out of the crustacean's side. "It's got no meat."

So Huynh (pronounced "Wynn") throws it over the side, where a small squadron of gulls and pelicans await. It was one of only three in his trap, one of about 300 he sets in the shallow waters of Mississippi Sound.

Huynh is one of the thousands of Vietnamese refugees who settled on the Gulf Coast for the fishing industry — but it's not much of a living these days. A few years ago, he was making upwards of $50,000 from the traps; now it's barely a quarter of that, he says. His wife works at a seafood processing plant onshore, but her hours are being cut back.

Mississippi crab fisherman Tam Huynh takes in a trap off Bay St. Louis as a seagull waits for any scraps.

Tam Huynh's haul of blue crab. Five years after the BP spill, fishermen like Huynh struggle with small catches.

It's never been an easy business. But in the five years since an undersea gusher erupted 40 miles to the south, Huynh and others say it's gotten far worse.

The April 20, 2010 explosion that sank the drill rig Deepwater Horizon, killing 11 men on board, led to the closure of much of the Gulf of Mexico to commercial fishing for that summer. Louisiana's rich coastal inlets bore the brunt of the oil, but Mississippi, Alabama, and parts of western Florida also saw crude wash up on their shores. The widespread use of a chemical dispersant to break up the oil has raised concerns that the combination of the two is far more toxic than either one alone.

Oil giant BP, which owned the well and has paid out over $30 billion for the spill, says there's no evidence that the spill has led to widespread fisheries losses and that the environmental catastrophe many feared has failed to materialize. Scientific studies so far have found only limited effects on marine life, and catch statistics Gulf-wide are roughly back to pre-spill levels.

"This strong recovery is in large part due to the Gulf's resilience, natural processes, and the effectiveness of response and clean-up efforts mounted by BP under the direction of the federal government," the company's lead spokesman, Geoff Morrell, said in a written statement. "We remain committed to restoring those natural resources that reliable data and science determine the spill injured."

But some once-productive fisheries remain deeply depressed. And while scientists say the reasons for the decline aren't entirely clear, the fishermen point the finger straight at the company.

"This is an oyster community, and it literally got destroyed because of BP," said Byron Encalade, an oysterman in Pointe a la Hache, Louisiana.

Mississippi crab fisherman Tam Huynh says he's thinking about taking a job as a deckhand on another boat because his catch has been so weak.

Boats out of the overwhelmingly African-American village Bay St. Louis, Mississippi, about 50 miles below New Orleans, work the oyster reefs east of the Mississippi River. Those reefs were devastated when Louisiana officials opened floodgates on the river in a bid to flush oil out of the state's rich coastal inlets — a desperate move that wrecked the balance of salt and fresh water that oysters need to survive.

Some of the decisions made during the spill "probably, in hindsight, were not the wisest," Fernando Galvez, a Louisiana State University environmental toxicologist who has studied the effect of oil on fish, told VICE News.

"Certainly, a lot of the areas that were high in oysters were also areas that were heavily hit by oil," Galvez said. "But I think you also have to consider the fact that these freshwater diversions had impacted these areas pretty dramatically."

The spillways opened again the year after the blowout, during a major Mississippi River flood. The Bonnet Carre spillway upriver from New Orleans poured water into Lake Pontchartrain, which flows out to the marshes and tidal basins of the East Bank — and into the west end of Mississippi Sound, where Huynh works.

Mississippi's oyster stocks — already wiped out by Hurricane Katrina six years earlier — collapsed again. In 2010, state fishermen delivered more than 300,000 hundred-pound oyster sacks to the docks; the count plummeted to 44,000 in 2011 and 65 in 2012.

But oystermen say they've seen that happen in previous floods, and the oysters usually come back in a year or two.

"The major production area east of the Mississippi hasn't come back at all. It's actually gotten worse," Matthew Slavich, a fifth-generation oysterman in Buras, Louisiana, told VICE News. The area's oyster season was cut to five days this year — and while those five days were a success, "Things are still very down."

Statewide, the tonnage of Louisiana oyster landings in the first three years after the spill are down about 18 percent from the 2000-2009 average, according to federal statistics. Figures for 2014 aren't yet available. Oyster hauls in Mississippi and Alabama are down, too.

"A lot of the older guys have gotten out," Slavich said. "If they were in a position to retire, they retired. Some of them sold out, and others are doing a bare-bones kind of business." Things are slowly improving, but the market "is struggling to survive," he said. "There's just not enough oysters."

Steve Murawski, a marine ecologist at the University of South Florida who has been studying the effects of the spill, said Gulf fisheries have been "a mixed bag" since 2010.

"Blue crab catches overall are about the same as they were pre-spill, but that doesn't mean that it's not localized," Murawski said. If patches of oil remain trapped in sediments near shore, where crabs live, that could be sickening the animals or hurting their reproduction.

Ruth Carmichael, who has studied both oysters and dolphins at Alabama's Dauphin Island Sea Lab, found in a 2012 study that oil had little effect on mature oysters — but oyster larvae haven't been extensively studied.

"Were past the stage of looking for necessarily acute, death-type responses in a lot of cases, but we're looking for some of the longer-term, population-level effects," Carmichael told VICE News. But she added that work could mean piecing together "multiple interacting factor" over years of observation.

"Just because we haven't seen something happen yet doesn't mean we think that we won't in the future," she said.